1. Field of the Invention
The invention concerns a control device for a polyphase synchronous rotary electrical machine.
More particularly, the invention concerns a control device for an AC-DC current converter associated with such a polyphase synchronous rotary electrical machine and arranged between it and an electrical storage unit consisting of a rechargeable battery.
2. Description of Related Art
It is especially suitable for reversible machines, known as alternator-starters, which are used in the automotive industry, both in alternator mode and in starter mode, or as an aid to moving off (boost mode), typically from 500 rpm.
Within the context of the invention, the term “polyphase” concerns, more specifically, three-phase or hexaphase rotary electrical machines, but may also concern biphase rotary electrical machines or those which operate at a higher number of phases.
For the sake of clarity, the following scenario relates to the preferred application of the invention, i.e. that of a reversible three-phase rotary electrical machine of the alternator-starter type, without this in any way limiting the scope of the invention.
As is well known, a reversible rotary electrical machine contains an alternator comprising:                a rotor constituting an inductor, traditionally combined with two collector rings and two brushes to supply an excitation current; and        a polyphase stator, bearing several coils or windings, three in the embodiment in question, constituting an armature, which are star-connected, or most often as a triangle, in the case of a three-phase structure, and which deliver converted electrical power to a bridge rectifier when operating as an alternator. The machine includes two bearings, a front and a rear, to fix it to the thermal engine and to fix the stator. The stator surrounds the rotor. The rotor is carried by a shaft supported by the front and rear bearings. The brushes are connected to a regulator of the alternator to maintain the voltage of the alternator at a desired voltage for a battery, depending whether it is on or off load.        
The alternator enables any rotation movement of the inductor rotor driven by the thermal engine of the vehicle to be transformed into an electrical current induced in the stator windings.
The alternator may also be reversible and constitute an electric motor, or rotary electrical machine, enabling the thermal engine of the vehicle to be driven in rotation via the rotor shaft. This reversible alternator is known as an alternator-starter, or alterno-starter. It enables mechanical energy to be transformed into electrical energy, and vice versa.
Thus, in alternator mode, the alternator-starter specifically charges the vehicle battery, while in starter mode, the alternator-starter engages the motor vehicle's thermal engine, also known as internal combustion engine, in order to start it.
In reversible machines from the automotive industry, for example, operating in motor or starter modes, the stator must be current-controlled in such a way that at any moment the necessary torque can be applied to the rotor to impel the required rotation for the operation of the engine. The torque applied to the rotor, and hence the current supplied to the phases of the stator, is a sinusoidal function of the angular position of the rotor in relation to the stator, represented by an angle θ.
FIG. 1, placed at the end of this description, illustrates in diagram form a complete system 1 for detecting the angular position θ(t) of the rotor of a three-phase alternator-starter and for controlling said organ, either in alternator mode or in engine (starter) mode.
The system 1 consists of four principal sub-systems: an alternator-starter 10, a reversible AC-DC current converter 11, a control module 13 for this converter and a module 12 for detecting the angular position θ of the rotor 100 (symbolized by an arrow turning about its axis of rotation Δ).
The converter 11 generally consists of a bridge of semiconductor rectifiers 110, comprising three branches of two MOSFET power transistors in series, 1101 to 1103, which will henceforth be referred to arbitrarily as “high” and “low”, one for each phase. A structure of this type is well known to the person skilled in the art and there is no need to describe it in further detail. The midpoints of the output branches, 1101 to 1103, constitute the three converter 11 outputs. The ends of the branches 1101 to 1103 are connected to the positive “+”, and negative “−” outputs of an electrical energy storage means, for example a battery Bat, with which the vehicle is fitted (not shown in FIG. 1).
In alternator mode, the alternator-starter 10 supplies the converter 11 with three-phase AC current via its three outputs, 101 to 103, which correspond to the junctions between the three coils constituting the stator 104 of the alternator-starter 10. The latter converts the three-phase AC current into DC current in order to (re)charge the battery Bat. This, in turn, supplies various organs of this vehicle: on-board electronics, air conditioning, headlights, etc.
FIG. 1A illustrates in more detail the configuration of the alternator-starter 10 from FIG. 1. The stator 104 contains three windings 1010 to 1030, in triangular configuration, the vertices of which are connected to the outputs 101 to 103.
In engine mode, i.e. in starter mode, it is the alternator-starter 10 which is supplied with three-phase electrical energy by the reversible converter 11, which is operating in three-phase current generator mode.
In this embodiment of the invention relating to a three-phase electrical machine and thus a three-branch transistor bridge, the MOSFET transistors of the branches 1101 to 1103 are controlled according to an appropriate sequence of six control signals, SC1 to SC6, regardless of whichever mode is under consideration. The six control signals, SC1 to SC6, are generated by the control module 13. As is also well known, these signals SC1 to SC6 must be generated synchronously with the angular position θ of the rotor 100 which detects the relative phases of the currents supplied by the outputs 101 to 103 of the alternator-starter 10 (alternator operating mode), or sent to these outputs (starter operating mode).
For this reason, it is necessary to detect the angular position θ of the rotor 100 with great precision, in order to achieve correct functioning of the bridge rectifiers 1101 to 1103, in particular to avoid any risk of deterioration of the semiconductor components, but also and above all, in engine or starter mode, to optimize the torque supplied by the alternator-starter 10.
This is the function which is devolved to the module 12 for detecting the angular position θ of the rotor 100 so as to generate a signal θ(t) representing the instantaneous variation of the measured angular position and to transmit it as an input to the control module 13.
In prior art, various methods have been proposed for this purpose.
In particular, the Applicant has proposed, in international patent application WO 2006/010864 A2, a device and a method for detecting the position of a rotor of a rotary electrical machine containing a stator, which makes it possible to obtain the precise angular position sought, while at the same time being cheap, simple to operate and having low sensitivity to magnetic interference.
The device taught in this patent application includes a plurality of magnetic field sensors fixed in relation to the stator of the rotary electrical machine and able to deliver a series of first signals representing a rotating magnetic field detected by these sensors, and means of processing these first signals by an operator able to provide a series of second sinusoidal signals depending on the angular position attained by the rotor.
In one embodiment, illustrated by FIG. 1 which is placed at the end of the present description, three linear Hall effect sensors CA1 to CA3 placed at 120° electric on the rotary electrical machine are used, in this case the alternator-starter 10, facing a target (not shown in FIG. 1) integral with the rotor 100 and magnetized alternately North/South for each pole of the machine. For a more detailed description, it would be advantageous to refer to the description in the previously cited international patent application WO 2006/010864 A2.
The sensors, CA1 to CA3, deliver a series of three signals CH1 to CH3 as output when the alternator-starter 10 is in rotation. It has been found experimentally that these signals, which are referred to as “raw”, usually contain a high level of harmonics, in particular a high level of harmonic 3, and their relative amplitudes are different. Hence, it is difficult to construct, from these three far from perfect raw signals, two signals which approach an ideal sinusoidal function (i.e. free from harmonics), with identical amplitudes, zero offsets and mutually phase-shifted in a non-obvious fashion (phase shift not a multiple of 180°), which constitute said second signals.
To alleviate this problem, the basic principle is to find two distinct linear combinations which enable the two sinusoids desired to be obtained, while at the same time finding the best possible solution to the problems raised above.
As a first approximation, it is possible to admit that the sensors CA1 to CA3 have identical, or at least very close, characteristics, that they are placed in an identical thermal and electromagnetic environment and thus that the signals delivered by these sensors retain some common characteristics. These hypotheses lead to the view that:                their offsets develop simultaneously depending on any interference field (such as, for example, magnetization of the rotor);        their levels of order 3 harmonics are very similar and in phase with their fundamental harmonics; and        the electrical signals generated by these sensors are phase-shifted by about 120°.        
These hypotheses make it possible to choose two linear combinations which partly cancel out the order 3 harmonics and the offsets. Simply by choosing, for linear combinations, the difference between two sensor output signals, one obtains two signals phase-shifted by 60° and which meet the selection criteria mentioned above.
It is then found that the signals obtained are close to ideal sinusoidal functions: they are reentered and contain fewer harmonics than the raw signals.
Nevertheless, the amplitudes of these signals are not completely identical and their offsets are not absolutely zero. This means that a factory calibration stage is required at the end of the manufacturing chain.
To do so, one may subtract an adjustable value from each of the signals in order to cancel each offset. This signed value can be obtained in purely analogue fashion, for example using a potentiometer or an adjustable resistive bridge (for example by using a procedure known as laser trimming) or semi-analogue, by using a digital value converted into an analogue value. Finally, a completely digital solution is also possible, if the signals are converted into digital signals.
With respect to amplitude calibration, a single adjustment is necessary, because it is sufficient for the signal amplitudes to be equal. To do so, a variable gain amplifier can be used. This variable gain amplifier can be purely analogue, semi-analogue or completely digital. It should be noted that the amplitude calibration could have been carried out in advance on two of the raw signals delivered by the sensors CA1 to CA3 so that later linear combinations are more effective in eliminating the order 3 harmonics. The disadvantage of this method lies in the fact that a supplementary adjustment is necessary and that it does not correct any disparities in amplification of the linear combinations themselves.
Once the two sinusoids have been obtained, it becomes possible to extract directly the value of the angular position θ. To do this, by dividing the two signals, one eliminates the amplitude, then, using a mathematical function or a table, the function can be inverted and the angular quadrant determined using the signs of the signals. For the sake of clarity, by way of non-limiting example, if the phase shift between signals is φ=90°, for example, this is an arctangent function. Again, for a more detailed description, it would be advantageous to refer back to the description in the previously cited international patent application WO 2006/010864 A2.
Within the scope of the invention, it is possible to make use of this method, or any other method known in the art, to detect the angular position θ of the rotor 100 with satisfactory precision.
The module 12 for detecting the angular position θ of the rotor 100 delivers at its output a signal θ(t) representing this angular position. This signal may be analogue in form, or, preferably, digital in form if the module 12 is provided with an analogue-digital conversion circuit (not shown).
The signal is transmitted as input to a control module 13 designed to generate a series of control signals for the switching members of the reversible AC-DC current converter 11, said switching members generally consisting of MOSFET power transistors 110, as already stated. In this case, which relates to a three-phase alternator-starter 10, the reversible converter 11 contains three branches of two MOSFET transistors in series, arranged between the “+” and the “−” poles of the battery Bat.
In this embodiment, for a three-phase electrical machine, the control module 13 therefore has to generate a series of six control signals, and these signals, SC1 to SC6, must be, as already stated, in perfect synchronization with the angular position θ of the rotor 100 which detects the relative phases of the currents delivered by the outputs, 101 to 103, of the alternator-starter 10, according to an appropriate timing sequence, so as to obtain a correct functioning of the rectifier bridges, in particular to avoid any risk of damage to the semiconductor components, but also, and above all, in engine or starter mode, optimized torque supplied by the alternator-starter 10.
Digital circuits enabling control signals of the “all or nothing” type to be generated, with square or rectangular configuration, are well known in the art.
However, the need has arisen, not only to be able to generate such signals, but also to be able to modify their configuration at will, in a very flexible way, without significantly increasing the cost and the complexity of the circuits of the control module 12, in particular to be able to change from a mode of operation referred to as “full wave” to another mode of operation, without having to substantially modify the circuits constituting this module, or even change them entirely (for example by substitution of a complete electronic circuit card or of the module itself by another).
As has already been said, within the scope of the invention the word “polyphase” refers without distinction to biphase, triphase or hexaphase machines, more generally functioning at a number of phases equal to n (being any whole number greater than 1). The need has therefore also arisen to be able to accommodate these diverse machines, whatever n may be, again without having to modify “materially” or change the circuits constituting the control module.